Snap action device



June 17, 1952 H. Ml LLARD 2,600,564

SNAP ACTION DEVICE Filed NOV. 7, 1947 F 1'47. 1 57 -56 +l4 7 r l lfl ,24 56 4 n.- ,2? 42 My 4/ V -26 Patented June 17, 1952 SNAP ACTION- DEVICE arp r Mfllard, er rt, L, ass non. ln'r i issne assignments, to Minneapolis-Honeywell Regu lator Company, Minneapolis, Minn., a. corpora:

tion oiDelawar Application November 17, 194 7, SeriaLNo. 7863494.

12 Claims.

This. invention relates to snap, action devices nd" m re particularly to devices havingthin leaf overcenterspring systems.

Although prior spring systems of the above character wh n: us d; on ele tric swi ches are commonly op rated for several: mi li f; per tionswith normai'current, interrupting canacity and give extremely satisfactory service, some applications require a spring construction which has a stillgreater life; expectancy and,- with a relatively higher current interruptingcapacity than has, heretofore been available ina switch of this type withoutv increasing;- the size; thereof. another diflioulty' encountered under some con ditions with certain structures of snap action devices utilizin sprin systems. of the bov character having spaced: stressed members and an intermediate interconnected stressed memberisthatin some instances, when; the plunger having; a, point. contact with the intermediate member-is actuated, one of. the spaced stressed members, may pass overcenter before the other. Thisisj particularly true ifthe pointv contactis to one si e of the lon itudinal; axis of: the intermediate stressed; member; Asa consequence; faulty operation of the devicel results in which thee'free endof the interconnected stressed member en a es both. stops. simultane usly. hich in the case of electric; switches effects burning or weldin of-the spring'and in turn causing failure of the switch resulting; in possible destruction f, or:- damaee, to, associated: apparatus.

Accordingly, it, is an object of this invention to; p ovid an mproved snap: shr ne; system: wit as nov l ar an ement and. prooorti nme t of the stre s d mem rs: formin he sn p pr n sy te n whi h effects a. switch co struction havin relatire v' high capacity and: a relativ ly" lon life.

Ano her bjec of; he v tion; s o provi e an mp ov d. nlun er o struction: whi h assures substantially simultaneous oivercenter movement f: the nacedi stressed: m mbers;

Another object of the invention is to provide an m roved swit h ns ruct on w ich isru d, which impl and: which is r la ively in xpenveto manu c ure:

Other objects and advantages of the invention will become apparent; from the following detailed description taken in connection with the accompanying drawings, in;- which-s Figure 1* is a. longitudinal" sectional view ofia snap action. switch. embodying the present invention;

Fig: 2 is; an: enlarged topview showing; a vsnap act n shrine, and ananch r slate for mounting h same;

Fig-. 3- ifsg ar planview: of a spring, staimgiilfieL Fig 4, is an enlarged sectional. view taken" sub;- stantially' along the; line- 1-4: of; Figure 12;; and

Fig; 5 is a. modification ofthe plunger. shown in Fig. 4,;

Referring nowto the: drawing-s the invention is, shown embodiedin; an electric switch. For purposes or illustration the; latter comprises a snapqspring; system I 1-, carrying a. contact (-2 for movement between preselected positions, mounted ina housing 3 i suitable insulatin material, and a-plunger mounted on thQrhQLSl' ing to actuate the snap: Spring; system: H.

The snap: spring; system, H herein is formed byspaced compression members- !6 and an intermediate; tension memberll. At: one enck the compression members l6 and, the tension;- mem ber l1 areintercoimected to; form an end his for supp rtin th con-tact l2" and fr e tomove between spaced fixed contacts t9; and 2t. 'l-Zhefl ter are formedv herein by spaced metal elements secured? to shoulders 22: and 23: respectively at one end ofpthe housing l3: as by screws M andgfi. The screws are threaded into.- conductine sleeves, such. assleeve 21% formed in the housing; Iii; and electrically; connected to a terminal: 29"on. the exterior-of; the housing; The terminal; 2-9; herein is secured to the-sleeve as by-a screw 3|. Whe re desired, one of the contacts [-9, and 2!; in. b omitted; and an insulating membersubstituted to fo ma st p: for the-conta t; t2.- Ih opposite ends of the; compression members L6; inthi's inr stanc areL niv ta y' supp rted in rooves" 32 f rmed at the ends of; less 33 of a u-sheocd anchor plate till-mounted; on av shoulder-35g fomed e d" of; the. h usin 1.3 opposite the; con tacts I8 and 21- as by a screw:- 36=. The latter screw: is threaded into a sleeve 3'! disposed in the housing l3 and to which issecured. a-te gmi-nal 38 on the exterior of the housing; as-zby a screw 39. Theroppositeendaof; thertensicn; meanber- H is fixedly moun ed in the ho in Inthis mbodiment of the invention a: cantilever mount.- ingor the tension member H is utilized: and is eifected-by securing the endrofthe tension mem ber H between a cross piece H of the anchor plate 34 and; a washer 42 held, in atightly; asisembled relation by the screw 35; Asv shown in Figure 1 the central portion of the cross piece 4| is offset relative to thepl'a'n'e of thelegs: 33 toform a recess for the end of-thetension member: IT supported thereon. V

One phase of the invention is concernedwith locating support means for the compression members I5 relative to the supported end of the tension member 47 and locating the position of the plunger on the tension member 11 so as to provide a switch construction with a relatively high mechanical weld breaking capacity, which primarily determines the rating of the switch, and at the same time having a relatively long life. To this end a snap spring construction is provided which is formed from suitable materials and in which the compressive force acts at a relatively large angle with respect to the tensile force so that a relatively large force is available for separating the normally open switch contacts. This is effected herein by utilizing a spring construction having a relatively long tension member l1, and relatively short compression members I 6 and utilizing relatively long legs 33 for supporting the compression members l6. One limit on the'length of the legs 33 is the compression members 15,

since the latter take a permanent set if they are bent beyond their elastic limit. Another limit on the length of the legs 33 is that spring'life expectancy is dependent upon the ratio between the length of the legs 33 to the point of support of length of the tension member I! has been found to be'3to 5. The length of the tension member I1 is measured from the point of overhang of the cantilever mounted tension member I! to the point'ofinterconnection between the compression and tension members [5 and I7 respectively. This is shown'as the distance A in Fig. 2. The length of the legs 33 which determines the position of the Support of the compression member 16 is measured from the point of overhang of the tension member I? to the grooves 32. This is shown as the distance B in Fig. 2.

Preferably the plunger 14 is located at a position which is approximately two-thirds of the distance from the point of overhang of the tension member I! to the support of the compression member [6 or the distance C shown in Fig. 2. In other words, the ratio of the distance of the plunger M from the mounting of the tension member I! to the length of the anchor leg 33 (designated by B on Fi 2) should be 2 to 3 for optimum operation. The upper limit for the ratio is rather sharply defined as 3 to 4. Thus, if the plunger position is changed in the direction toward the free ends of the legs 33 it has been found that in operating the switch there is a tendency for sizzling and dead-break at the contacts l9 and 2! respectively. Furthermore this location of the plunger it provides a switch con- .operation and eventually reach a point where the snap spring system i i fails to operate.

-A specific example of a switch structure embodying the invention, comprises a stamping 43 -.(see Fig. 3) of beryllium copper, measuring .0065

inch to .0075 inch in thickness. The formed stamping is heat treated in the usual manner to have a tensile strength of 185,000 to 195,000 pounds per square inch and a Rockwell hardness of 79 to 81 on the 15N scale. The overall length, M, of the stamping 43, as shown, is 1 inches. Using a centerline M of a mounting hole 45, .0995 inch, plus .003 inch, minus .000 inch in diameter and having its axis spaced g inch in from the end of the tension member 17, the respective parts of the stamping have the following dimensions measured in the plane of the stamping before assembly: the distance, N, between the centerline 44 and a centerline 47 of the opening for the contact 12 is 1.297 inches, plus or minus .003 inch; the distance, 0, between the centerline 44 and the interconnection 48 of the tension member I! and compression members 15 is 15 inches; the distance, P, between the extreme free ends 49 of the compression members l5 and the centerline 44 is .710 inch, plus .000 inch, minus .002 inch; the overall Width, Q, of the stamping is .500 inch, plus or minus .0025 inch; the width, R, of the compression members 16 is .109 inch, plus or minus .003 inch the width, S, of the central portion of the tension member I7 is .156 inch, plus or minus .003 inch; and the width of the end portion in which the mounting hole is formed is .218 inch, plus or minus .002 inch.

The anchor plate 34 to be used with a spring stamping of the dimensions specified above is formed as a metal stamping from brass material measuring .064 inch in thickness, plus or minus .002 inch. The free ends of the legs 33 are grooved to form recesses as herein described for the squared ends of the compression members 16. In its finished form the length of the legs 33 measured from the mounting hole (through which the screw 36 extends) .101 inch in diameter, plus or minus .0015 inch, spaced inwardly from the side of the member 4| .093 inch, plus or minus .001 inch, to the bottom of the grooves is' .740 inch, plus or minus .022 inch. The overall Width of the anchor plate is .550 inch, plus or minus .003 inch. The width dimension of the anchor 34 at the grooves may be slightly larger due to displacement of material in forming the grooves. It is to be understood that the specific dimensions set forth are not limiting values and are applicable only to the specific embodiment shown herein.

Another phase of the invention is directed to a plunger is construction that effects substantially simultaneous overcenter movement of both spaced stressed members It. For this purpose the plunger is formed with a head 5| (see Figs. 4 and 5) having a projection 52 with a surface 53 shaped to engage the tension member I! along a line substantially perpendicular to the longitudinal axis of the tension member 11. The plunger i4 is positioned and guided in its axial movement by an elongated portion 55 projecting through a snug fitting guideway 56 formed in a cover 51 on the housing l3. To insure that the contact surface 53 of the plunger 14 does not rotate relative to the tension member 11, the plunger 14 is formed with an intermediate skirt portion 59 integral with the head 5! which is shaped to fit between the walls 59 of the housing I 3 to prevent rotation of the plunger 14. In the present instance the plunger is formed as a single unit in which the elongated portion 54 is secured to a washer Bl which in turn is secured to the head portion 5i. In Fig. 5 there is shown another construction of the plunger 14. As shown the head 5| of the plunger I4. is formed. withv two. projections. 62: in spaced: relation and: shaped. tov engage the. ten.- sion; member H at positions spaced adjacent each edge. of. the latter member. It is to be understood that either of the above constructions prevent turning movement of the tension member l-l. about its longitudinal axis as it is moved through the axis of maximum stress when the spring system is actuated. Either of'these'constructions assures a snap spring construction in which both sides of the snap spring system act concurrently.

I claim:

1. In a. snap action device, the combination of" a support, a snap spring comprising spaced compression members and an intermediate tension member, said spaced compression-members and said tension member being interconnected at one end to form an end free to move between opposed positions, means for mounting the opposite end of said tension member, an anchor plate including spaced legs adjacent opposite sides of the mounted end of the tension member for mounting the opposite ends of said compression members, said tension and compression members inthe mounted position being stressed to form a snap spring system having an axis of maximum stress and a plunger mounted on said support and having spaced projections for engaging said tension member at spaced positions on a line extending transversely of said tension member, said plunge being shaped to move said tension member without rotation thereof about a longitudinal axis, through the axis of maximum stress whereby to move said free end between the opposed positions with a snap action.

2'. In a snap. action device, the combination of a support, a snap spring comprising spaced compression members and an intermediate tension member, said spacedcompression members and said tension member being interconnected atone end to form an end free. to move between opposed positions, means for mounting the opposite end of said tension. member, an anchor plate including spaced legs adjacent opposite. sides of the mounted end of the tension member for mounting the opposite ends of said compression members, said tension and compression members in the mounted position being stressed to form a snap spring system having, an axis of maximum stress, a plunger mounted on. said support for engaging said tension member with a line contact, said line contact extending transversely of said tension member and substantially perpendicular to the longitudinal axis thereof, said plunger being operable to move said tension member through the axis of maximum stress whereby to move said free end between the opposed positions with a snap action and means for preventing rotation of the plunger.

3. In a snap action device. the combination of a support, a tension member mounted on said support and having a free end movable between preselected positions, an anchor mounted on said support, a compression member having one end supported on said anchor and the opposite end interconnected with the free end of the tension member, said tension member and said. compression member formin a snap spring system having an axis of maximum stress, the distance between said supported end of the compression member and the mounted portion of the tension member as compared to the length of said tension member being in substantially the ratio of 3 to member, and. means for mounting the opposite ends-of. said. compression member, the distance to the. point 'of support of the compressionmember measured from themounting means of said tension member and the length of said tension member being in. the ratio of approximately 3 to 5.

5. In a snapaction device, the combination of a support, a tension member havin oneof its ends mounted on. said support and having its other end free to'move' between opposed positions, a compression member having one end interconnected with the free end of the tension member and the opposite end in spaced relation with said mounted end of the tension member,

means for supporting said opposite endof the compression member, the distance from said latter support. means for the opposite end of said compression member to the mounted end of. the

tension member and the length of the tension member from the-same point on the mounted end of the tension member to the point ofinterconnection with the compression member being in the ratio of 3 to 5, said tension member and said compression. member forming an overcenter snap spring system, and meansengageable with said tension member for moving said'spring system overcenter whereby said free end moves between said preselected positions with a snap action.

6'. In a snap action device, the combination of a base, spaced stops mounted thereon, an overcenter snap spring having an axis of maximum stress and formedv by spaced compression members and an intermediate tension member, said spaced compression members and said tension memberbeing interconnected at. one end to form an end free to move between the opposed stops with a snap action, means for'mounting the opposite end of said tension member, an anchor plateincluding spaced legsadjacent opposite sides of the mounted end of the tension member for mountin the opposite ends of said compression members, the distance on saidlegs to the point of support of the compression members measured from the mounting means of said tension member and the length of said tension member'lbeing in the ratio of approximately 3 to 5, and

means engageable with saidtension member for moving it through the axis of maximum stress whereby to move said free end between, the stops.

7. In a snap action device, the combination of a, snap spring system. having an axis, of maximum stress comprisinga tension member having a supported end and an. end free to move between preselected positions, and a compression member having one end interconnected with said free end of the tension member and having an opposite end in spaced relation with the supported end of the tension member, means for supporting said opposite end of the compression member, said supporting means being located at a position substantially three-fifths of the distance between the supported end of the tension. member and the interconnection between the tension member and the compression member from the supported end of the tension member, and means engaging said tension member at a position substantially two-thirds of the distance from the supported end of the tension member to the supporting means for said compression member from the supported end for moving the tension member through the axis of maximum stress whereby to move said free end between opposed positions with a snap action.

8. In a snap action device, the combination of a snap spring system having an axis of maximum stress comprising a tension member having a supported end and an end free to move between preselected positions with a. snap action when the tension member moves through the axis of maximum stress, and spaced compression members having one end interconnected with said free end of the tension member and having their opposite ends in spaced relation with the supported end of the tension member, means for supporting said opposite ends of the compression members, said supporting means being located at a position substantially three-fifths of the distance between the supported end of the tension member and the interconnection between the tension member and the compression members from the suported end of the tension member, and means engaging said tension member at a position substantially two-thirds of the distance from the supported end of the tension member to the supporting means for said compression member from the supported end and shaped to engage said tension member whereby to prevent rotation of said tension member about its longitudinal axis as the latter moves through the axis of maximum stress.

9. In a snap acting device, the combination of a snap spring system comprising spaced first stressed members and a second stressed member, said spaced stressed members and said second stressed member being interconnected at one end to form an end free to move between opposed positions, means for mounting the opposite end of said second stressed member, an anchor plate comprising spaced legs adjacent opposite sides of the mounted end of the second stressed member for supporting the opposite ends of said spaced stressed members, said point the second stressed member and the spaced L stressed members from the mounted end of said second stressed member, said stressed members in the mounted position being stressed to form a snap spring system having an axis of maximum stress, and a plunger having a portion engaging one side of said second stressed member with line contact along a line extending transversely of said second stressed member substantially two-thirds of the distance from the mounted end of the second stressed member to the point of support for said spaced stressed members from the mounted end of said second stressed members, said portion positioned to extend substantially perpendicular to the longitudinal axis thereof, said plunger being operable to move said second stressed member through the axis of maximum stress whereby said free end moves between opposed positions with a snap action.

10. In a snap action device, the combination of a support, a snap spring comprising spaced compression members and an intermediate tension member arranged in edgewise spaced relationship, said spaced compression members and said tension member being interconnected at one end to form an end free to move between opposed positions, means for mounting the opposite end of said tension member, an anchor plate secured adjacent the mounted end of the tension member including spaced legs extending longitudinally of and in edgewise spaced relation to opposite sides of the tension member for mounting the opposite ends of said compression members, said tension and compression members in the mounted position being stressed to form a snap spring system having an axis of maximum stress and a plunger mounted on said support having a portion shaped for reception between said spaced legs, the end of sad portion having a shape to engage the tension member along a line extending transversely thereof to move the tension member through the axis of maximum stress without rotation thereof about a longitudinal axis upon movement of the tension member by the plunger and to resist rotation of the tension member about a longitudinal axis upon return movement of the tension member.

11. In a snap action device, the combination of a leaf spring comprising tension and compression members joined at an end free to move, a support for mounting the other end of the tension member, and means for pivotally mounting the other end of the compression member to stress the compression member in bowed compression, the distance between the mounting for the compression member and the support for the tension member being to the length of the tension member from its support substantially in the ratio of .3 to 5.

12. The combination recited in claim 11, further characterized by a plunger positioned to engage the tension member at substantially twothirds of the distance from its support to the mounting for the compression member for moving the tension member through an axis of maximum stress with the compression member.

HARPER MILLARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,493,559 Norden May 13, 1924 1,960,020 McGall May 22, 1934 2,044,822 Vaughn June 23, 1936 2,153,716 Kelley Apr. 11, 1939 2,181,068 Riche Nov. 21, 1939 2,182,856 Riche Dec. 12, 1939 

